Synchronizing-signal separating apparatus



April 21, i942. J. c. "WILSON SYNCHRON'IVZING S IGAL SEPARATING APPARATUS Filed July 13, `1940 N O S L RW O. T N E V m ATTORNEYY Patented Apr. 21, 1942 t t SYN CHRONIZING-SIGNAL t r `APPARATU John C. Wilson, Bayside, N.

s SEPARATING Y., assignor to `Hazeltine Corporation, a corporation of Dela- Ware Application July13, 1940, Serial No. 345,289 Y 1o claims. (ci. 17a-7.5)

This invention relates generally to synchronizing apparatus `for television receivers.

Various arrangements have been heretofore proposed for the separation `of synchronizing signals from a composite received television signal and their use in televisionreceivers. ventional television signal comprises a vision signal and a composite synchronizing signal including line-synchronizing pulses and a plurality of field-synchronizing pulses during each fieldunderlap interval of the same polarity as, but of greater duration than, the line-synchronizing pulses. As used in this specication, the term eld-underlap interval" is intended to mean the interval between elds during which no video information is translated by the system. In order accurately to synchronize the field-scanning oscillator, it is necessary to separate the field-synchronizing pulses from the composite synchronizing signal. Certain types of field-synchronizingsignal separating arrangements which have been utilized in prior art television upon the integration of the composite synchronizing signal to derive a signal for synchronizing the field-'scanning operation of the receiver.A This type of synchronizing-signal separator has an advantage in that it is relatively impervious to disturbing noise signals but may have the disadvantage that the timing of the signal derived therefrom is not as accurate as desired.

Another type Aof eld-synchronizing-signal separator which has been used in prior art arrangements depends for its operation upon the differentiation of the eld-synchronizing signal to derive a signal responsive to the leading or trailing edges of the pulses of the field-synchronizing signal. This last-mentioned type of synchronizing-signal separator, while providing very accurate timing, may be subject to tion due to noise impulses which may be present with sufiicient amplitude and energy content to disturb the operation of the system. Such s'ystems inherently operate on the small amount of energy which can be derived from an edge of the composite synchronizing signal. It is desirable, however, to provide a held-synchronizing-signal separator which contains the desirable attributes of both of the above-mentioned types.

The cont receivers depend faulty operafrom an edge of one of the Held-synchronizing pulses. However, in such prior art systems also, the derived signal depends only upon the small amount of energy procured from the edge oi"-a synchronizing pulse and, therefore, such systems may be subject to faulty operation due to noise components which are present in the composite signal. It is desirable, therefore, to provide a eld-synchronizing-signal separator, the sensitivity of which depends upon an integration or a storing of energy from the composite synchronizing signal 'and which need not be rendered so sensitive that its operation depends entirely upon the energy derived from an edge of a field-synchronizing pulse. That is, it is desirable to provide a system of the general type under discussion in which a substantial part of the energy of a relatively broad field-synchronizing pulse is available for initiating the scanning operation of the system.

It is an object of the presentinvention, therefore, to provide an improved held-synchronizingsignal separating apparatus not subject to the above-mentioned disadvantages of prior art arrangements.

It is a further object of the invention to provide an improved eld-synchronizing-signal separating apparatus in which a double immunity is provided against interference or noise signals except for a very short time immediately prior to the occurrence of the portion of the signal by which synchronizing is to be effected.

It is still another object of the invention to provide an improved field-synchronizing-signal separating apparatus of the general type under discussion which need not be so sensitive that its operation depends entirely rived from an edge of a held-synchronizing pulse.

Prior art systems also have been proposed in which the sensitivity of the field-synchronizing-- integration of signal separator depends upon an the composite synchronizing signal while the timing of the signal derived from the signal separator depends upon a differentiation of the composite signal, that is, upon energy derived of the held-synchronizing pulses.

further provided responsive to the In accordancewith the invention, there is provided in a television signal-translating systemla synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality of eld-synchronizing pulses for each eld-underlap interval of the same polarity as,

but having a greater duration than the line-synchronizing pulses comprising means including an integrating circuit responsive to a predetermined one of the held-synchronizing pulses of each eld-underlap interval and substantially unresponsive to the line-synchronizing pulses deriving a sensitizing signal initiating at the trailing edge of the above-mentioned predetermined one Means are above-menupon the energy deoscillator-modulator 'and intermediate-frequency ampliiier Fig. l of the drawing is a circuit diagram,

partly schematic, ceiver ofthe superheterodyne type embodying a television synchronizng-signal-separating apparatus in accordance with the present invention, while Fig. 2 comprises a series of graphs utilized to explain the operation of the circuit of Fig. 1.

Referring now more particularly to Fig. 1 of the drawing, the system there represented comprises a receiver of the superheterodyne type including an antenna system I0, II connected to a radio-frequency amplifierl2, to which are connected in cascade, in the order named, an

I3, an intermediate-frequency amplifier I4, a vision-signal detector and A. V. C. supply I5, a video-frequency amplifier I6, and an image-reproducing device I1. A linescanning circuit I8 and a eld-scanning circuit I9 are provided, each having an input circuit coupled to the output circuit of detector I5 through a synchronizing-signal separator 20, the eld-scanning circuit I9 being coupled to synchronizing-signal separator 20 through a fieldsynchronizing-signal separator 2I constructed in accordance with the present invention and pres- .ently to be described in detail. The output circuits of line-scanning circuit I8 and Held-scanning circuit I3 are coupled to the scanning elements of image-reproducing device I1 in a manner well understood in the art. A sound-signal l detector and amplier 22 and a sound-signal reproducing device 23 are coupled to the output circuit of intermediate-frequency amplifier I4. An automatic amplication control potential derived from detector I5 is applied over conductor A. V. C. to one or more of the tubes of radiofrequency amplifier I2, oscillator-modulatlor I;

'maintain the amplitude of the signal input to the detector I5 and to the detector stage of unit v22.within relatively narrow limits for a wide range of received signal amplitudes. The stages or units Ill- 23, inclusive, excepting unit 2I presently. to be described in detail, may be of conventional well-known construction so. that detailed illustration and description thereof are deemed unnecessary herein.

Referring briefly, however, to the operation of the system described above,.television signals intercepted by antenna. circuit I0, II are selected and amplified in radio-frequency amplifier I2 and translated to the oscillator-modulator I3, wherein they are converted into intermediatefrequency signals which, in turn, are selectively4 amplified in the intermediate-frequency amplifier I4 and from which the vision-modulated signal is delivered to thel detector I5. The vision-modulation components of the signal are derived by the detector I5 and are supplied to the video-frequency amplifier I6, wherein they are amplilled and from which they are supplied, in the usual manner, to a brightness-control elecoi a complete television re' signal separator 20. The intensity of the scanning beam of the device I1 is thus modulated or controlled in accordance with the video-frequency voltages impressed upon its control electrode in the usual manner. Scanning waves are generated in.the line-scanning and field-scanning circuits I8 and I9, respectively, which are controlled by synchronizing-voltage pulses derlved from detector I5, and applied to the scanning elements of the image-reproducing device I1 to produce electric scanning fields to deflect the scanning beam in two directions normal to each other, so as to trace a rectilinear scanning pattern on the screen and thereby reconstruct the transmitted image. Sound-modulated signals derived from intermediate-frequency amplifier I4 are detected and amplified in unit 22 and reproduced in unit 23 in a conventional manner. The A. V. C. potential derived from detector I5 and applied to stages I27 I3, and I4 serves to maintain the signal input to detector I5 and to the detector stage of unit 22 within a relatively narrow amplitude range for a Wide range of received signal amplitudes,

Referring now more particularly to the portion of the system embodying the present invention, fleld-synchronizing-signal separator 2I is adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality of field-synchronizing pulses for each eld-underlap interval of the same polarity as, but having a greater duration than, linesynchronizing pulses and comprises energystorage means for integrating the composite syntrode of the image-reproducing device I1 and a to the synchronizing-control elements of scanchronlzing signal, derived from synchronizingsignal separator 20, to derive a iirst sensitzing signal during each fleldl-underlap interval. This integrating means comprises a resistor 30 connected in series with a parallel-connected resistor 3l and condenser 32, the sensitzing signal derived from the circuit 3|, 32 being applied to an outer control grid of a multigrid vacuum-tube repeater 33. The composite synchronizing signal derived from synchronizing-signal separator 20 is also applied to an inner control grid of vacuum tube 33 by means of a coupling condenser 34 and grid-leak resistor 35, vacuum tube 33 being provided with an output circuit including load resistor 36. Suitable unidirectional operating potentials are provided for the several electrodes of vacuum tube 33 by means of unidirectional sources C, Ci, -I-Sc, and +B, tube 33 being normally biased to cutoff,

'I'he synchronizing-signal separating unit 2| also includes a quickly-responsive and slowly-recovering means including an integrating circuit responsive to a predetermined one of the eldsynchronizing pulses of each eld-underlap inter val and substantially unresponsive to the linesynchronizing pulses and dependent upon the first sensitzing signal derived by the resistance-condenser network 30, 3|, 32 for deriving a second sensitzing signal initiating at the trailing edge of the predetermined one of the field-synchronizing pulses. 'I'his last-mentioned means comprises an integrating circuit responsive to the field-synchronizing pulses of the composite signal and substantially unresponsive to the line-synchronizing pulses thereof, the circuit including a diode 38 coupled across the load resistor 36 of tube 33 through coupling condensers 39 and 40, a resistor 4I being connected in parallel with condenser 40 through a unidirectional-voltage source C2. In order to provide means responsive-jointly to the sensitzing signal and to the field-synchronizing synchronizing-signal separator 2|.

\ `nizing pulses F Yduring outer control grid thereof is coupled directly to the load circuit of vacuum tube 33 through coupling condenser 39 and a grid-leak resistor 44', a load circuit including resistor 45 being provided for tube 44. Suitable unidirectional operating potentials are provided for vacuum tube 44 by means of a source C2, source Ca, and sources +Sc and +B in a manner well understood in the art.

Reference is made to the curves of Fig. 2 for an explanation of the operation of the system of Fig. 1 constituting the present invention. In curve A of Fig. 2, there is illustrated a portion of the composite synchronizing signal derived from synchronizing-signal separator 2l and applied to ileld- This composite synchronizing signal comprises a linesynchronizing pulse L and a plurality oi' eldsynchronizing pulses F, F

of the same polarity as, but having a greater duration than, the linesynchronizing pulse L. 'I'he resistance-condenser network 30, 3| 32 is so, proportioned that the voltage developed across condenser 32 rises to a substantially constant level during the tlrst fieldsynchronizing pulse F of each field-underlap interval as illustrated by curve B of Fig. 2 and a voltage of this wave form is, therefore, applied to the outer control grid of vacuum tube 33; that is, condenser 321s charged substantially to the maximum voltage represented by the field-synchrothe time interval represented by the iirst held-synchronizing pulse of each eld-underlap interval. Such control grid of vacuum tube 33 is so biased by means of uni.- directional source C that the tube is nonconductive in the absence of the sensitizing signal derived from resistance-condenser network 3|), 3|, 32 but becomes conductive in the presence of such sensitizing pulse, for instance, at an amplitude such as is represented by the dotted line C oi' Fig. 2. Therefore; it is seen that, at the beginning of each of the ileld-underlap intervals, tube 33 is nonconductive and is rendered conductive by the sensitizing pulse B derived during the field-underlap interval. Tube 33 is` thereafter effective to pass the remaining broad held-synchronizing pulses of the eld-underiap interval applied to its inner control grid and is output current and an output voltage across load resistor 36 of the waveformy illustrated adjacent the anode of tube 33.

` Diode 33 and its associated load circuit comprising condenser 40 and resistor 4| provides a quickly-responsive and slowly-recovering means or an energy-storage device including a short time-constant charging circuit and a long timeto the inner control grid of vacuum tube 44 which, in turn, is so biased by means of source Cz that it is cu oil' for control'potentials applied to its inner control grid below the amplitude level represented by dotted line E of Fig. 2. The rise of potential across condenser 40, as represented by curve D,

therefore, unblocks the inner control grid of tube 44 in time for the second` and succeeding fieldsynchronizing pulses to be passed by tube 44, the resulting voltage G developed across load resistor 45 being utilized ing circuit i9 accurately on the leading edge of the second field-synchronizing pulse.

It is, therefore, seen that diode 38, condenser '40, and resistor 4| effectively comprises a means which is quickly-responsive and slowly-recovering and which is dependent upon the first sensitizing signal, that is, the signal represented by curve B for deriving a second sensitizing pulse, curve D.

initiating at the trailing edge oi' a predetermined one of the field-synchronizing pulses of each fieldunderlap interval. Specifically, in the embodiment illustrated, the second sensitizing signal initiates at the trailing edge of the ilrst of the -field-synchronizing pulses of each ileld-underlap interval. Vacuum tube 44 thus comprises a means dependent upon the first and secondsensitizing signals for deriving a control signal from thefield-synchronizing pulse following the trailing edge of the ilrst field-synchronizing pulse.

It is thus seen that, in the embodiment disclosed, the field-synchronizing-signal separator iii effective to develop an constant discharging circuit, the condenser 40 l being Veffectively charged substantially instantaneously upon the occurrence of the rst positive step in the output Wave of tube 38, which corresponds in time with the trailing edge of the first held-synchronizing pulse F, by virtueof the low internal resistance of diode 38. e time constant of the diode load circuit inctlygrig condenser 40 and resistor 4| is relatively yl ng so that condenser 40 is not substantially/discharged during the succeeding field-synchronizing pulses. There is thus developed across condenser 40 a voltage of the wave form of curve ,D' of Fig. i2 which is applied 2| is effective to deliver a control signal for synchronizing the scanning operation of the receiver which initiates at the leading edge of'the second field-synchronizing pulse of curve A, thus to provide accurate timing of the operation of fieldscanning circuit |3. It will be understood, however, that field-scanning circuit I3 need not depend entirely for its synchronization upon energy derived from an edge of a synchronizing pulse,

because the whole of the energy of the ileldsynchronizing pulseof curve A following the nrst pulse is available for synchronizing the lleidscanning circuit |3.

Furthermore, it will be understood that tube 44 comprises an arrangement responsive to the sensitizing .pulse D and to the composite synchronizing signal for deriving the desired control voltage and that in other embodiments of the invention the composite synchronizing signal can be applied directly to tube 44 rather than being applied through tube 33. Y

While there has been described what is at present considered to be the preferred embodiment .of this invention, it will be'obvious to those skilled in the art that various changes and modiiications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modiilcations as fall within the true spirit and scope o'f the invention.

What is claimedA is:

VJ. vIn a television signal-translating system, a `synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchroni-ing pulses and a plurality of field-synchronizing pulses for each ileld-"nderlap interval of the samepolarit'r as. but having a greater duration than. said linesvnchroni'finar pulses comprising, means including an integrating circuit responsive to a predeterrnined one of said ileld-synchronizingpulses of each field-underlap interval` and substantially unresponsive to said line-synchronizing pulses to synchronize field-synchronizfor deriving a sensitizing signal initiating at the trailing edge of said predetermined one of said field-synchronizing pulses, and means responsive jointly to said sensitizing signal and to the fieldsynchronizing pulse of said composite synchronizing signal for deriving a control signal from the eld-synclironizing pulse following said trailing edge.

2. In a television signal-translating system, a synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality of field-synchronizing pulses for each eld-underlap interval of the same polarity as, but having a greater duration than, said linesynchronizing pulses comprising, means including an integrating circuit responsive to the first of said field-synchronizingpulses of each eldunderlap interval and substantially unresponsive to said line-synchronizing pulses for deriving a sensitizing signal initiating at the trailing edge of said rst of said field-synchronizing pulses, and means responsive jointly to said sensitizing signal and to the field-synchronizing pulses of said composite synchronizing signal for deriving a control signal from the second field-synchronizing pulse of each eld-underlap interval.

3. In a television signal-translating system, a synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality f eld-synchronizing pulses for each eld-underlap interval of the same polarity as, but having a greater duration than, said linesynchronizing pulses comprising, means including an integrating circuit responsive to a predetermined one of said field-synchronizing pulses of each eld-underlap interval and substantially unresponsive to said line-synchronizing pulses for deriving a sensitizing signal initiating at the trailing edge of said predetermined one of said eld-synchronizing pulses, and means responsive jointly to said sensitizing signal and to the fieldsynchronizing pulses of said composite synchronizing signal for deriving a control signal initiating at the leading edge of the field-synchronizing pulse following said trailing edge.

4. In a television signal-translating system, a synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality of field-synchronizing pulses for each eld-underlap interval of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means including an integrating circuit responsive to the field-synchronizing pulses of said composite signal and substantially unresponsive to the linesynchronizing pulses thereof for deriving a'irst sensitizing signal during each field-underlap interval, means responsive to said first sensitizing signal for deriving a second sensitizing signal initiating at the trailing edge of a predetermined one of said field-synchronizing pulses of each ield-underlap interval, and means responsive jointly to said rst and second sensitizing signals for deriving a control signal from the fieldsynchronizng pulse following said trailing edge.

5. In a television signal-translating system, a synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality of field-synchronizing pulses for each eld-underlap interval of the same polarity as, but having a greater duration than, said linesynchronizing pulses comprising, means including an integrating circuit responsive to the fieldsynchronizing pulses of said composite signal and substantially unresponsive to the linesynchronizing pulses thereof for deriving a rst sensitizing signal during each field-underlap interval, an energy-storage device including a short time-constant charging circuit and a long time-constant discharging circuit responsive to said\f`1rst sensitizing signal for deriving a second sensitizing signal initiating at the trailing edge of a predetermined one of said field-synchronizing pulses of each eld-underlap interval, and means responsive jointly to said rst and second sensitizing signals for deriving a control signal from the field-synchronizing pulse following said trailing edge.

6. In a television signal-translating system, a synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality of field-synchronizing pulses for each field-under ap interval of the same polarity as, but having greater duration than, said linesynchronizing p lses comprising, a resistor-condenser network responsive to the field-synchronizing pulses of said composite signal and substantially unresponsive to the line-synchronizing pulses thereof for deriving a rst sensitizing signal during each field-underlap interval, means responsive to said first sensitizing signal for deriving a second sensitizing signal initiating at the trailing edge of a predetermined one of said eldsynchronizing pulses of each feld-underlap interval, and means jointly responsive to said first and second sensitizing signals for deriving a control signal frorn the field-synchronizing pulse following said trailing edge.

7. In a television signal-translating system, a synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality of eld-synchronizing pulses for each eld-underlap interval of the same polarity as, but having a greater duration than, said linesynchronizing pulses comprising, means including a resistor connected in series with a parallelconnected resistor and condenser responsive to the field-synchronizing pulses of said composite signal and substantially unresponsive to the line-synchronizing pulses thereof for deriving a rst sensitizing signal during each field-underlap interval, means responsive to said rst sensitizing signal for deriving a second sensitizing signal initiating at the trailing edge of a predetermined one of said field-synchronizing pulses of each field-underlap interval, and means jointly responsive to said rst and second sensitizing signals for deriving a control signal from the field-synchronizing pulse following said trailing edge.

8. In a television signal-translating system, a synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality of field-synchronizing pulses for each eld-underlap interval of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means for integrating said composite signal to derive a first sensitizing signal during each field-underlap interval, means including a diode connected in series with a parallel-connected resistor and condenser and responsive to said first sensitizing signal for derivinga second sensitizing signal iniof said field-synchronizing pulses of each fieldunderlap interval, and means responsive jointly to `said first and second sensitizing signals for deriving a control'signal from the iield-synchronizing pulse following said trailing edge.

9. In a televisionI signal-translating system, a synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality of field-synchronizing pulses for each eld-underlap interval of the same polarity as, but having a greater duration than, said linesynchronizing pulses comprising, means for integrating said composite signal to derive' a first sensitizing signal during each `ield-underlap interval, a vacuum tube normally biased to cutoff, means for utilizing said :lirst sensitizing signal for sensitizing said vacuum tube, means coupled to the output circuit of said vacuum tube for deriving a second sensitizing signal initiating at ve trailing edge of a predetermined one lof said field-synchronizing pulses of each iield-underlap interval, and means responsive jointly to said first and second sensitizing signals for deriving a control signal from the tieni-synchronizing pulse following said trailing edge.

10. In a television signal-translating system, a synchronizing-signal separating apparatus adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and a plurality of field-synchronizing pulses for each fleld-underlap interval of the same polarity as, but having a greater duration than, said linesynchronizing pulses comprising, means for integrating said composite signal to derive' a rst l sensitizing signal during each field-underlap interval, quickly-responsive and slowly-recovering 

